Bill Simpson claims that this idea is ~10 years old, but if so perhaps it's time to air it again. I thought of this during the route flap BOF at NANOG, mentioned it, and nobody came up with any immediate reasons why it wouldn't work, so I'm sending it to the list for further consideration. It's dead simple, really: Assign address blocks to pairs of providers. Both providers announce those blocks all the time, and assign addresses out of those blocks to customers who multihome between those two providers. Now, clearly this won't help all multihomed nets, because you can't possibly provide netblocks for all provider pairs- you'd have n*n-1 blocks instead of n, for n providers- but you can optimize for common cases. In particular, any two providers who will state that they are going to coordinate multihoming get a netblock. You can also limit this, at least in the beginning, to some smallish group of providers (such as the big six/seven/whatever, though that's probably a poor criterion). Any provider who wants to start doing this today can, of course, simply by declaring that part of its aggregate is now jointly owned by another provider, and that other provider announcing that part. This isn't really a change in technology so much as it is a change in bookkeeping: by putting all the multihomed nets together, both of the providers of those multihomed nets can aggregate announcements. But the benefit is real: fewer routes, and no route flaps when any single multihomed customer falls off the net. You reach breakeven on # of routes as soon as any pair of providers has two customers doing multihoming. That makes this scheme beneficial both to customers and to providers. So, any takers? /a